This project is an investigation into the mechanism and structure of the (Na ion plus K ion)-ATPase. Studies are proceeding along the following lines: (a) measurements of the transient kinetics of the phosphorylation and dephosphorylation of the (Na ion plus K ion)-ATPase; (b) experiments designed to determine the subunit structure and stoichiometry of the functional unit of the (Na ion plus K ion)-ATPase; (c) studies to determine the stoichiometries of ligand-binding in relation to the subunit structure of the (Na ion plus K ion)-ATPase; (d) investigations into the possible existence of endogenous regulatory components acting upon the (Na ion plus K ion)-ATPase in brain and other tissues; (e) studies of the relation of enzyme phosphorylation to the conformational transition of the enzyme cycle; (f) studies of the kinetic properties of the ATP hydrolysis catalysed by the (Na ion plus K ion)-ATPase in the absence of K ion.